翻转二叉树

给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */
 
function invertTree(root: TreeNode | null): TreeNode | null {
    //递归的进行翻转即可
    if(root === null || root === undefined ) return null
    const right =root.right
    const left = root.left
    root.left = right ? invertTree(right) : null
    root.right = left ?  invertTree(left) : null
    return root
};